1. Field of The Invention
This invention relates to cutting-free bronze alloys which are substantially free of lead and which exhibit good castability and a good corrosion resistance. The alloys are adapted for use in various fields such as of plumbing faucets and fixtures for water supply for general-purpose pipings, and sliding members employed in a corrosive atmosphere such as of fresh water or sea water. The alloys are also suitable as a material which is employed when it is desirable to improve machinability, soundness in texture, pressure resistance and anti-seizing property while eliminating the injury from lead.
2. Description of the Prior Art
In general, characteristic requirements for constituent materials of plumbing faucets and fixtures for water supply for general-purpose pipings (hereinafter referred to generically as cock fixtures) include (1) good flowability because of the adoption of a casting method which is used to make complicated shapes, (2) good soundness in texture for preventing detrimental porosity which is liable to occur owing to the possible irregularity in thickness, (3) high mechanical strength and a good pressure resistance since no water leakage is permitted on use as a cock fixture, (5) good machinability because of a great number of portions to be worked, and (6) a good resistance to corrosion through dezincification since the fixture is employed in contact with water supply, waters or sea water and should thus have a good corrosion resistance. Moreover, when used as sliding members which are used in contact with fresh water or sea water and should have a good corrosion resistance, such a constituent material should effectively prevent corrosion through dezincification. The constituent material should also have a good anti-seizing property in order to ensure good sliding characteristics. In order to almost satisfy these requirements, usual practice is to use brass or bronze materials.
However, the conventionally employed materials as mentioned above have the following problems which should be overcome. Brass materials utilized for the plumbing faucets and fixtures include, for example, JIS.H.3250.C3604, C3771 (cutting-free brasses), which contain large amounts of lead. Thus, the injury from lead is not avoidable. In fact, when they are in contact with water, corrosion through dezincification inevitably takes place. Another type of brass material such as JIS.H.3250.C4641 is known as preventing corrosion through dezincification. This brass material contains no lead, so that the machinability is not satisfactory. Although cutting-free brass materials which prevent corrosion through dezincification are commercially sold, they contain lead, thereby causing injury from lead. In addition, cutting-free brass materials wherein lead is substituted with bismuth are known. However, no tin is added to the materials, so that the corrosion through dezincification is liable to occur, coupled with another problem that the materials contain a misch metal and is thus expensive (Japanese Laid-open Patent Application No. 5-255778).
Moreover, U.S. Pat. No. 5167726 discloses a cutting-free brass wherein lead is substituted with bismuth, but expensive indium is also contained therein, resulting in high costs. A further type of brass which contains phosphorus in place of indium is known. However, phosphorus reacts with iron in the starting materials, thereby creating hard spots in the resultant brass. This, in turn, requires the use of starting materials which have to be substantially free of any metals adversely influencing the brass alloy, thus inviting a rise in cost. On the other hand, bronze materials which are utilized as a plumbing faucet and fixture include, for example, JIS.H.5111.BC1, BC6 and BC7. These materials have good castability, soundness in texture and machinability along with a satisfactory pressure resistance. However, the bronze materials contain a large amount of lead, thereby presenting the problem of injury from lead. Moreover, other types of bronze materials are known including, for example, JIS.H.5111.BC2, BC3. Although these types of materials contain not larger than 1 wt. % of lead, lead is not positively incorporated as an additive element. More particularly, the content of lead in these materials is less than that of lead-containing bronzes, thus leading to poorer machinability. Japanese Patent Publication No. 5-63536 discloses a material wherein lead in lead bronzes is replaced by bismuth to prevent injury from lead and improve the machinability and castability. However, a multitude of pores are formed at the time of casting, thereby impeding the soundness in texture. In addition, this material is poorer in pressure resistance and mechanical strength than lead-containing bronzes. Hence, limitation is placed on the use of the material as articles which are simple in shape and which are relatively uniform in thickness. Furthermore, the material disclosed in Japanese Patent Publication No. 5-279771 has a similar problem as in Japanese Patent Publication No. 5-63536, coupled with another problem that it contains a misch metal and is thus expensive.
Next, the materials utilized as sliding members include, for example, aluminium bronze materials such as JIS.H.5114.AlBC1, AlBC2 and AlBC3. These materials undergo corrosion through dealuminization and are low in anti-seizing property and poor in machinability. In contrast, brass which is set out, for example, in Japanese Laid-open Patent Application No. 63-16456 is admixed with 0.5 to 2 wt % of tin in order not to cause corrosion through dezincification and further with bismuth in place of lead thereby improving machinability. Moreover, in order to improve a wear resistance, 1.0 to 10.0 wt % of graphite is added. For the uniform dispersion of the graphite, a mold has to be used, which places limitation on the shape of articles along with an additional cost of the mold. On the other hand, phosphorus bronze is known including JIS.H.5113.PBC2. This bronze does not cause any corrosion through dezincification and has a satisfactory wear resistance. Because neither lead nor bismuth is added to the material, it is poor in machinability and is worse in anti-seizing property than similar bronze alloys containing lead. Moreover, a material called CDA915, wherein nickel and lead are added to the phosphorus bronze material, is known and has been in wide use as a material for gears. This material is excellent in wear resistance and corrosion resistance through dezincification but is injured from lead owing to the presence thereof.
The term xe2x80x9cinjury from leadxe2x80x9d used herein is intended to mean injuries of human body or environments caused from lead. More particularly, the problems involved at the time of fabrication of articles during the course of high temperature working operations such as liquation or dissolution, casting and welding include the formation of metallic fumes containing lead. Likewise, the problems caused during the course of working processes such as cutting, polishing and the like include the formation of metallic dust or powder. In the use of the resultant articles, another problem is involved in that lead is liable to dissolve out from portions contacting with water and that worn dust is inevitably produced at sliding portions.
As is apparent from the above, most of the alloys produced in the prior art contain lead, and thus, present injurious problems of lead to the human body and environment. If, however, alloys which are free of any lead in order to prevent injury from lead are used, machinability, anti-seizing property and pressure resistance become poorer than those of lead-containing alloys. This places limitations on the types of articles to be fabricated or utilized. The substitution of lead with bismuth can solve these disadvantages and will make it possible to improve the machinability and anti-seizing property to an extent comparable to those of lead-containing materials. However, such materials have a great number of pores produced at the time of casting and are thus inferior in pressure resistance and mechanical strength to lead-containing materials.
It is accordingly an object of the invention to provide a bronze alloy which is substantially free of any injury from lead and has good machinability, anti-seizing property and pressure resistance.
It is another object of the invention to provide a bronze alloy which is satisfactory with respect to castability, soundness in texture, resistance to corrosion through dezincification, wear resistance and the like.
In a broad aspect, the above objects can be achieved, according to a first embodiment of the invention, by a cutting-free bronze alloy which comprises 1 to 13 wt % of tin, not greater than 18 wt % of zinc, 0.5 to 6 wt % of bismuth, 0.05 to 3 wt % of antimony, not greater than 1 wt % of phosphorus, less than 0.4 wt % of lead, and the balance being copper.
Since the alloy defined above comprises less than 0.4 wt % of lead, the injury from lead can be prevented at the time of fabrication or use of articles of the alloy. A small amount of bismuth added to the alloy can improve machinability and anti-seizing property while ensuring the soundness in texture. Antimony serves to suppress formation of pores at the time of fabrication and ensures the soundness along with the pressure resistance and mechanical strength being improved. Tin is effective in preventing corrosion through dezincification. The castability of the alloy is improved by addition of zinc and phosphorus, and the wear resistance and mechanical strength can be improved by means of zinc and phosphorus along with tin. In this manner, the alloy of the invention is prevented from the injury from lead and exhibits good machinability, anti-seizing property and pressure resistance along with other satisfactory characteristics such as castability, soundness, a resistance to corrosion through dezincification, and a wear resistance. Thus, the alloy is particularly suitable for use as plumbing faucets and fixtures and sliding members.
Preferably, the alloy further comprises from 0.1 to 3 wt % of nickel. When nickel is added in such an amount as defined above, the alloy is reinforced as a matrix and is appropriately prevented from segregation.
According to a second embodiment of the invention, there is preferably provided a cutting-free bronze alloy which comprises 3 to 8 wt % of tin, 6 to 10 wt % of zinc, 0.5 to 6 wt % of bismuth, 0.5 to 2 wt % of antimony, 0.001 to 0.5 wt % of phosphorus, less than 0.2 wt % of lead and the balance being copper.
In the above-defined alloy, tin is present in an amount of 3 to 8 wt %, so that the alloy has both good mechanical strength and a good resistance to corrosion through dezincification. Since the contents of zinc and phosphorus are, respectively, in the ranges of 2 to 10 wt % and 0.001 to 0.5 wt %, better castability is ensured. This is very suitable for fabricating castings having a complicated shape such as bib cocks. Moreover, antimony is present in an amount of 0.1 to 2 wt %, so that the resultant alloy is more improved in toughness and mechanical strength and is enhanced in soundness while suppressing the porosity. In this case, it is more preferred to add nickel in amounts of 0.1 to 3 wt % as in the first embodiment for the same reasons as set out hereinabove.
According to a third preferred embodiment of the invention, there is provided a cutting-free bronze alloy which comprises 8.5 to 13 wt % of tin, not greater than 1 wt % of zinc, 0.5 to 6 wt % of bismuth, 0.05 to 3 wt % of antimony, 0.05 to 1 wt % of phosphorus, less than 0.4 wt % of lead and the balance being copper.
Since 8.5 to 13 wt % of tin, not greater than 1 wt % of zinc and 0.05 to 1 wt % of phosphorus are present, the resultant alloy is more improved in wear resistance and is optimum for use as a sliding member, e.g. a worm wheel, which is employed under severe conditions. The alloy should more preferably comprise nickel in amounts of 0.1 to 3 wt % for similar reasons as having set out hereinabove.